Common rail fuel systems typically employ multiple injectors connected to a common rail that is provided with high pressure fuel. In order to efficiently accommodate different combinations of injections at a variety of timings and injection amounts, the systems generally include a variable discharge pump in fluid communication with the common rail. One type of variable discharge pump is a cam driven, inlet- or outlet-metered pump.
A cam driven, inlet- or outlet-metered pump generally includes multiple plungers, each plunger being disposed within an individual pumping chamber. The plunger is connected to a lobed cam by way of a follower such that, as a crankshaft of an associated engine rotates, the cam likewise rotates and the connected lobe(s) reciprocatingly drives the plunger to displace (i.e., pump) fuel from the pumping chamber into the common rail. The amount of fuel pumped by the plunger into the common rail depends on the amount of fuel metered into the pumping chamber prior to the displacing movement of the plunger, or the amount of fluid spilled to a low-pressure reservoir during the displacing stroke of the plunger.
The variable discharge pump may be utilized to cancel or dampen vibration and noise. That is, by varying the displacement of fuel, a resulting torque may be transferred in reverse direction to the cam, thereby reducing and/or canceling vibration and noise. However, determining and controlling the timings and displacement of the fuel to cancel or reduce vibration can be difficult.
One attempt at reducing engine vibration is described in U.S. Pat. No. 5,111,748 (the '748 patent), issued to Kuriyama et al. on May 12, 1992. The '748 patent discloses an apparatus that induces vibrations in an alternator to reduce vibrations of a vehicle engine and a vehicle body due to irregular engine combustion. Specifically, the '748 patent changes the torque load of the alternator, which is fixed to the engine, to create an angle moment on the body of the alternator. This angle moment is transferred to the engine and reduces engine vibration. In particular, a voltage higher than the output voltage of the alternator is applied to field windings to change the torque load in response to a change in engine speed. Thus, when the alternator vibrations and the engine vibrations are in an inverse phase relationship, the vibrations from the alternator may cancel the vibrations from the engine.
Although the apparatus disclosed in the '748 patent may help minimize engine vibrations, it may have a limited range. That is, an alternator may be very limited in what vibrational amplitude and period it can create. Thus, the alternator vibration may be too little to affect large amplitude vibrations initiated within the engine.